Piezoelectric actuator and method of manufacture therefor, and ink jet head and ink jet type recording device

ABSTRACT

A piezoelectric actuator  21  has: a piezoelectric actuator part  22  made up of a common electrode  27 , a piezoelectric element  29 , and an individual electrode  33 ; an electrical interconnection joint part  43  formed on the individual electrode  33 ; an electrical interconnection  45  formed on the electrical interconnection joint part  43 ; a head block  47  fixed to a nozzle plate  39  through the electrical interconnection  45 ; and a PI tape  49  disposed within the head block  47 . A closed space  57  is defined between the head block  47  and the nozzle plate  39 . The closed space  57  is divided by the PI tape  49  into two sections. Of these two sections of the closed space  57 , the one on the side of the head block  47  constitutes a first closed space  57   a . A moisture absorbent  52  is sealed within the first closed space  57   a . Relative humidity within the closed space  57  of the ink jet head  1  is not less than 0% nor more than 20%.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/462,357 filed on Jun. 16, 2003 now U.S. Pat. No. 6,921,157. Thisapplication also claims the benefit of Japanese Patent Application Nos.2002-181402 filed Jun. 21, 2002. The disclosure(s) of the aboveapplication(s) are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to piezoelectric actuators and methods ofmanufacture therefor, and to ink jet heads and ink jet type recordingdevices.

BACKGROUND ART

Ink jet heads cable of effecting recording by making utilization of thepiezoelectric effect of piezoelectric elements have been known in theprior art.

A typical ink jet head of such a type has a piezoelectric actuatorformed by laminating together a common electrode, a piezoelectricelement, and an individual electrode in sequence, and an ink flow pathsubstrate in which is formed a pressure chamber. Mounted on one surfaceof the piezoelectric actuator is a vibrating plate. The vibrating plateis bonded onto an ink flow path formation substrate with an adhesiveagent. And, during the emission of ink, voltage is impressed on thecommon electrode and on the individual electrode, as a result of whichthe piezoelectric element undergoes expansion and contraction. Thevibrating plate restricts the expansion and contraction of thepiezoelectric element. Consequently, the piezoelectric actuatorundergoes bending and deformation in the lamination direction. Thevolume of the pressure chamber is varied by the bending and deformationof the piezoelectric actuator, and ink in the pressure chamber is shotthrough a nozzle.

Incidentally, piezoelectric elements are formed of insulating material.Therefore, it is undesirable for the ink jet head to be left in humidcircumstances for the following reasons. A typical piezoelectric elementis prepared by a film forming technique such as sputtering or the like.This, however, may give rise to a void and/or a pinhole within thepiezoelectric element in the course of such film preparation. Voids arelikely to be produced by the abnormal growth of a piezoelectric elementcaused by contaminants adhering onto an ink flow path substrate. On theother hand, pinholes are likely to be produced when a piezoelectricelement is sputtered onto an ink flow path formation substrate. And, ifmoisture enters a void or a pinhole, this results in increased leakcurrent when voltage is impressed between both the electrodes.Therefore, there is the possibility of occurrence of dielectricbreakdown.

With a view to eliminating the above-mentioned harmful effects, JapanesePatent Kokai Gazette No. (1999)235823 proposes an ink jet head providedwith a cap for enclosing a piezoelectric element which is joined onto anink flow path formation substrate, thereby making it possible to preventwater vapor from entering the space within the cap. Consequently,entrance of water vapor into a void or a pinhole of the piezoelectricelement is prevented, and it can be expected that dielectric breakdowndue to moisture will be prevented from occurring.

The above-described ink jet head construction is provided with a capcapable of enclosing a piezoelectric actuator. However, it does notprovide any means for absorbing moisture within the cap, thereforemaking it difficult to maintain the space within the cap at low humiditylevels. Consequently, there is still the possibility of occurrence ofdielectric breakdown in the above-described prior art ink jet head.

In order to eliminate the above-mentioned harmful effects, JapanesePatent Publication No. 2754407 proposes a piezoelectric actuatorprovided with a moisture absorbing part having a moisture absorbingaction. This moisture absorbing part is disposed in the vicinity of apiezoelectric element. Therefore, ambient humidity around thepiezoelectric element is lowered by the moisture absorbing action of themoisture absorbing part, and it can be expected that dielectricbreakdown due to moisture will be prevented from occurring.

The above-described piezoelectric actuator construction includes amoisture absorbing part in the vicinity of a piezoelectric element.However, it does not provide any means for isolating the piezoelectricactuator itself from moisture-containing outside air. In addition, theforegoing patent publication fails to provide any means for coping withproblems arising when the moisture absorption action of the moistureabsorption part becomes deteriorated. Therefore, it is difficult for theabove-described piezoelectric actuator to maintain ambient humidityaround the piezoelectric element at low levels. Therefore, there is thepossibility of occurrence of dielectric breakdown.

Bearing in mind the foregoing drawbacks with the prior art techniques,the present invention was made. Accordingly, an object of the presentinvention is to prevent dielectric breakdown due to moisture fromoccurring in a piezoelectric actuator by specifying relative humidityaround the piezoelectric actuator, the performance of a moistureabsorbent, or the performance of a cap member enclosing thepiezoelectric actuator.

DISCLOSURE OF INVENTION

A first invention is a piezoelectric actuator comprising: apiezoelectric actuator main body having a bottom electrode, apiezoelectric element formed on the bottom electrode, and a topelectrode, formed on the piezoelectric element, for impressing voltageon the piezoelectric element together with the bottom electrode; and ahumidity control device for maintaining, at the time of such voltageimpression, ambient relative humidity around the piezoelectric actuatormain body at not less than 0% nor more than 20% in a measurementenvironment of 60° C. and 1 atm.

Such arrangement further ensures that dielectric breakdown due tomoisture is prevented from occurring.

A second invention is a piezoelectric actuator comprising: apiezoelectric actuator main body having a bottom electrode, apiezoelectric element formed on the bottom electrode, and a topelectrode, formed on the piezoelectric element, for impressing voltageon the piezoelectric element together with the bottom electrode; a capmember for enclosing at least a surface of the piezoelectric actuatormain body on the side of the top electrode; and a moisture absorbentdisposed in a closed space between the piezoelectric actuator main bodyand the cap member and having an ability to absorb moisture, whereinambient relative humidity within the closed space is not less than 0%nor more than 20% in a measurement environment of 60° C. and 1 atm.

As a result of such arrangement, ambient relative humidity around thepiezoelectric actuator main body is maintained at not less than 0% normore than 20% in a measurement environment of 60° C. and 1 atm, wherebydielectric breakdown due to moisture is prevented from occurring.

A third invention is a piezoelectric actuator comprising: apiezoelectric actuator main body having a bottom electrode, apiezoelectric element formed on the bottom electrode, and a topelectrode, formed on the piezoelectric element, for impressing voltageon the piezoelectric element together with the bottom electrode; a capmember for enclosing at least a surface of the piezoelectric actuatormain body on the side of the top electrode; and a moisture absorbentdisposed in a closed space between the piezoelectric actuator main bodyand the cap member and having, as an indication of the efficiency ofabsorbing moisture, a coefficient of moisture absorption of not lessthan 5 wt. % in a measurement environment of 25° C., 1 atm, and 80%relative humidity, wherein the amount of moisture absorbed into themoisture absorbent is not less than 0 wt. % nor more than 20 wt. %.

Incidentally, when relative humidity within a closed space is at lowlevels, the amount of absorbable moisture is small. Therefore, theamount of moisture absorbable by a moisture absorbent is reduced. Statedanother way, there is found a correlation between the amount ofabsorbing moisture and the relative humidity. Here, in accordance withthe present invention, the amount of moisture absorption by the moistureabsorbent is not less than 0 wt. % nor more than 20 wt. % and, as aresult, the relative humidity within the closed space is held at lowlevels. Accordingly, dielectric breakdown due to moisture is preventedfrom occurring.

A fourth invention is a piezoelectric actuator comprising: apiezoelectric actuator main body having a bottom electrode, apiezoelectric element formed on the bottom electrode, and a topelectrode, formed on the piezoelectric element, for impressing voltageon the piezoelectric element together with the bottom electrode; a capmember for enclosing at least a surface of the piezoelectric actuatormain body on the side of the top electrode; and a moisture absorbentdisposed in a closed space between the piezoelectric actuator main bodyand the cap member and having an ability to absorb moisture, wherein thecap member has, in an interior surface thereof, a water vaporpermeability of not more than 7 g/m²·24 hr·atm.

As a result of such arrangement, the permeability of water vapor in theinterior surface of the cap member is not more than 7 g/m²·24 hr·atm,therefore preventing entrance of moisture from outside the closed spaceinto the closed space. Accordingly, dielectric breakdown due to moistureis prevented from occurring.

A fifth invention is a piezoelectric actuator comprising: apiezoelectric actuator main body having a bottom electrode, apiezoelectric element formed on the bottom electrode, and a topelectrode, formed on the piezoelectric element, for impressing voltageon the piezoelectric element together with the bottom electrode; a capmember for enclosing at least a surface of the piezoelectric actuatormain body on the side of the top electrode; a dividing member disposedwithin the cap member and dividing a closed space between thepiezoelectric actuator main body and the cap member into a first closedspace without the piezoelectric actuator main body, and a second closedspace which contains the piezoelectric actuator main body; and amoisture absorbent disposed in the first closed space and having anability to absorb moisture.

As a result of such arrangement, the moisture absorbent is disposed inthe first closed space which does not contain the piezoelectric actuatormain body, therefore preventing the moisture absorbent and thepiezoelectric actuator main body from coming into contact with eachother. Accordingly, possible damage to the piezoelectric actuator mainbody caused by the moisture absorbent is avoided.

In a sixth invention according to the fifth invention, the dividingmember supports the moisture absorbent.

Such arrangement eliminates the need for separate provision of asupporting means for supporting the moisture absorbent because themoisture absorbent is supported by the dividing member. Accordingly, thenumber of component parts of the piezoelectric actuator is reduced.

In a seventh invention according to the fifth invention, the dividingmember is formed of a resin material.

Such arrangement makes it possible to change the shape of the dividingmember with ease because the dividing member is formed of resinmaterial. Accordingly, the dividing member can be disposed within thecap member by changing the shape of the dividing member in conformity tothe shape of the cap member, regardless of the shape of cap member.Accordingly, the dividing member is disposed within the cap member withease.

In an eighth invention according to the fifth invention, one or morethrough holes are formed through the dividing member for communicationbetween the first closed space and the second closed space.

The dividing member is provided with one or more through holes forcommunication between the first closed space and second closed space,thereby enabling the moisture absorbent disposed in the first closedspace to efficiently absorb moisture within the second closed spacethrough the through holes. Accordingly, dielectric breakdown due tomoisture is effectively prevented from occurring.

In a ninth invention according to the second invention, thepiezoelectric actuator main body is subjected to a dehumidificationprocess before the piezoelectric actuator main body is enclosed by thecap member.

Since, prior to the piezoelectric actuator main body being enclosed bythe cap member, the piezoelectric actuator main body is subjected to adehumidification process, this makes it possible to preremove, even whenmoisture has already entered a void or a pinhole produced within thepiezoelectric element, the moisture before the piezoelectric actuatormain body is enclosed by the cap member. Accordingly, dielectricbreakdown due to moisture is effectively prevented from occurring.

In a tenth invention according to the third invention, the piezoelectricactuator main body is subjected to a dehumidification process before thepiezoelectric actuator main body is enclosed by the cap member.

Accordingly, the tenth invention provides the sameoperation/working-effect that the ninth invention provides.

In an eleventh invention according to the fourth invention, thepiezoelectric actuator main body is subjected to a dehumidificationprocess before the piezoelectric actuator main body is enclosed by thecap member.

Accordingly, the eleventh invention provides the sameoperation/working-effect that the ninth invention provides.

In a twelfth invention according to the fifth invention, thepiezoelectric actuator main body is subjected to a dehumidificationprocess before the piezoelectric actuator main body is enclosed by thecap member.

Accordingly, the twelfth invention provides the sameoperation/working-effect that the ninth invention provides.

In a thirteenth invention according to the ninth invention, thedehumidification process comprises either a process of heating thepiezoelectric actuator main body or a process of evacuating air from thepiezoelectric actuator main body under vacuum.

The piezoelectric actuator main body is heated or air evacuated undervacuum, which makes it possible to preremove, even when moisture hasalready entered a void or a pinhole produced within the piezoelectricelement, the moisture before the piezoelectric actuator main body isenclosed by the cap member. Accordingly, dielectric breakdown due tomoisture is effectively prevented from occurring.

In a fourteenth invention according to the tenth invention, thedehumidification process comprises either a process of heating thepiezoelectric actuator main body or a process of evacuating air from thepiezoelectric actuator main body under vacuum.

Accordingly, the fourteenth invention provides the sameoperation/working-effect that the thirteenth invention provides.

In a fifteenth invention according to the eleventh invention, thedehumidification process comprises either a process of heating thepiezoelectric actuator main body or a process of evacuating air from thepiezoelectric actuator main body under vacuum.

Accordingly, the fifteenth invention provides the sameoperation/working-effect that the thirteenth invention provides.

In a sixteenth invention according to the twelfth invention, thedehumidification process comprises either a process of heating thepiezoelectric actuator main body or a process of evacuating air from thepiezoelectric actuator main body under vacuum.

Accordingly, the sixteenth invention provides the sameoperation/working-effect that the thirteenth invention provides.

In a seventeenth invention according to the second invention, a humiditylowering process in which the piezoelectric actuator main body is leftas it is until the moisture absorbent absorbs a predetermined amount ofmoisture in the closed space is carried out after the piezoelectricactuator main body is enclosed by the cap member.

Since, after the piezoelectric actuator main body is enclosed by the capmember, the piezoelectric actuator main body is subjected to a humiditylowering process in which the piezoelectric actuator main body is letstand until the moisture absorbent absorbs a predetermined amount ofmoisture in the closed space, this makes it possible to remove moisturewithin the closed space by the time the ink jet head is put in use.Accordingly, dielectric breakdown due to moisture is effectivelyprevented from occurring.

In an eighteenth invention according to the third invention, a humiditylowering process in which the piezoelectric actuator main body is leftas it is until the moisture absorbent absorbs a predetermined amount ofmoisture in the closed space is carried out after the piezoelectricactuator main body is enclosed by the cap member.

Accordingly, the eighteenth invention provides the sameoperation/working-effect that the seventeenth invention provides.

In a nineteenth invention according to the fourth invention, a humiditylowering process in which the piezoelectric actuator main body is leftas it is until the moisture absorbent absorbs a predetermined amount ofmoisture in the closed space is carried out after the piezoelectricactuator main body is enclosed by the cap member.

Accordingly, the nineteenth invention provides the sameoperation/working-effect that the seventeenth invention provides.

In a twentieth invention according to the fifth invention, a humiditylowering process in which the piezoelectric actuator main body is leftas it is until the moisture absorbent absorbs a predetermined amount ofmoisture in the closed space is carried out after the piezoelectricactuator main body is enclosed by the cap member.

Accordingly, the twentieth invention provides the sameoperation/working-effect that the seventeenth invention provides.

In a twenty-first invention according to the second invention, the capmember is formed of a metal.

Such arrangement that the cap member is formed of a metal makes itpossible to prevent entrance of moisture from outside the closed spaceinto the closed space. Accordingly, dielectric breakdown due to moistureis effectively prevented from occurring.

In a twenty-second invention according to the third invention, the capmember is formed of a metal.

Accordingly, the twenty-second invention provides the sameoperation/working-effect that the twenty-first invention provides.

In a twenty-third invention according to the fourth invention, the capmember is formed of a metal.

Accordingly, the twenty-third invention provides the sameoperation/working-effect that the twenty-first invention provides.

In a twenty-fourth invention according to the fifth invention, the capmember is formed of a metal.

Accordingly, the twenty-fourth invention provides the sameoperation/working-effect that the twenty-first invention provides.

In a twenty-fifth invention according to the second invention, the capmember is fixed onto a surface of the piezoelectric actuator main body.

Such arrangement that the cap member is fixed onto the surface of thepiezoelectric actuator main body eliminates the need for separateprovision of a cap-member fixing means. Accordingly, the number ofcomponent parts of the piezoelectric actuator is reduced.

In a twenty-sixth invention according to the third invention, the capmember is fixed onto a surface of the piezoelectric actuator main body.

Accordingly, the twenty-sixth invention provides the sameoperation/working-effect that the twenty-fifth invention provides.

In a twenty-seventh invention according to the fourth invention, the capmember is fixed onto a surface of the piezoelectric actuator main body.

Accordingly, the twenty-seventh invention provides the sameoperation/working-effect that the twenty-fifth invention provides.

In a twenty-eighth invention according to the fifth invention, the capmember is fixed onto a surface of the piezoelectric actuator main body.

Accordingly, the twenty-eighth invention provides the sameoperation/working-effect that the twenty-fifth invention provides.

In a twenty-ninth invention according to the twenty-fifth invention, thepiezoelectric actuator further comprises an electrode interconnection,formed on the top electrode, for transmission of electrical signals tothe top electrode, wherein the electrode interconnection is interposedbetween the cap member and a surface of the piezoelectric actuator mainbody.

Such arrangement that the electrode interconnection is interposedbetween the cap member and the surface of the piezoelectric actuatormain body makes it possible to prevent the cap member and thepiezoelectric actuator main body from coming into contact with eachother at a point where the electrode interconnection is interposedbetween the cap member and the piezoelectric actuator main body surface.Accordingly, it is possible to prevent the cap member from interferingwith the operation of the piezoelectric actuator main body.

In a thirtieth invention according to the twenty-sixth invention, thepiezoelectric actuator further comprises an electrode interconnection,formed on the top electrode, for transmission of electrical signals tothe top electrode, wherein the electrode interconnection is interposedbetween the cap member and a surface of the piezoelectric actuator mainbody.

Accordingly, the thirtieth invention provides the sameoperation/working-effect that the twenty-ninth invention provides.

In a thirty-first invention according to the twenty-seventh invention,the piezoelectric actuator further comprises an electrodeinterconnection, formed on the top electrode, for transmission ofelectrical signals to the top electrode, wherein the electrodeinterconnection is interposed between the cap member and a surface ofthe piezoelectric actuator main body.

Accordingly, the thirty-first invention provides the sameoperation/working-effect that the twenty-ninth invention provides.

In a thirty-second invention according to the twenty-eighth invention,the piezoelectric actuator further comprises an electrodeinterconnection, formed on the top electrode, for transmission ofelectrical signals to the top electrode, wherein the electrodeinterconnection is interposed between the cap member and a surface ofthe piezoelectric actuator main body.

Accordingly, the thirty-second invention provides the sameoperation/working-effect that the twenty-ninth invention provides.

A thirty-third invention is an ink jet head comprising a piezoelectricactuator as set forth in the first invention.

A thirty-fourth invention is an ink jet head comprising a piezoelectricactuator as set forth in the second invention.

A thirty-fifth invention is an ink jet head comprising a piezoelectricactuator as set forth in the third invention.

A thirty-sixth invention is an ink jet head comprising a piezoelectricactuator as set forth in the fourth invention.

A thirty-seventh invention is an ink jet head comprising a piezoelectricactuator as set forth in the fifth invention.

A thirty-eighth invention is an ink jet head comprising a piezoelectricactuator as set forth in the second invention, and an ink flow pathforming member formed on a lower surface of the bottom electrode andhaving an ink flow path therein, wherein the cap member is fixed onto asurface of the ink flow path forming member.

Such arrangement that the cap member is fixed onto the surface of theink flow path forming member eliminates the need for separate provisionof a cap member fixing means. Accordingly, the number of component partsof the ink jet head is reduced.

A thirty-ninth invention is an ink jet head comprising a piezoelectricactuator as set forth in the third invention, and an ink flow pathforming member formed on a lower surface of the bottom electrode andhaving an ink flow path therein, wherein the cap member is fixed onto asurface of the ink flow path forming member.

Accordingly, the thirty-ninth invention provides the sameoperation/working-effect that the thirty-eighth invention provides.

A fortieth invention is an ink jet head comprising a piezoelectricactuator as set forth in the fourth invention, and an ink flow pathforming member formed on a lower surface of the bottom electrode andhaving an ink flow path therein, wherein the cap member is fixed onto asurface of the ink flow path forming member.

Accordingly, the fortieth invention provides the sameoperation/working-effect that the thirty-eighth invention provides.

A forty-first invention is an ink jet head comprising a piezoelectricactuator as set forth in the fifth invention, and an ink flow pathforming member formed on a lower surface of the bottom electrode andhaving an ink flow path therein, wherein the cap member is fixed onto asurface of the ink flow path forming member.

Accordingly, the forty-first invention provides the sameoperation/working-effect that the thirty-eighth invention provides.

In a forty-second invention according to the thirty-eighth invention, astep portion is formed in an upper peripheral area of the ink flow pathforming member and the cap member fits with the step portion of the inkflow path forming member.

Since the cap member fits with the step portion of the ink flow pathforming member, the cap member and the piezoelectric actuator main bodyare in non-contact with each other. Accordingly, it is possible toprevent the cap member from interfering with the operation of thepiezoelectric actuator main body.

In a forty-third invention according to the thirty-ninth invention, astep portion is formed in an upper peripheral area of the ink flow pathforming member and the cap member fits with the step portion of the inkflow path forming member.

Accordingly, the forty-third invention provides the sameoperation/working-effect that the forty-second invention provides.

In a forty-fourth invention according to the fortieth invention, a stepportion is formed in an upper peripheral area of the ink flow pathforming member and the cap member fits with the step portion of the inkflow path forming member.

Accordingly, the forty-fourth invention provides the sameoperation/working-effect that the forty-second invention provides.

In a forty-fifth invention according to the forty-first invention, astep portion is formed in an upper peripheral area of the ink flow pathforming member and the cap member fits with the step portion of the inkflow path forming member.

Accordingly, the forty-fifth invention provides the sameoperation/working-effect that the forty-second invention provides.

A forty-sixth invention is an ink jet head comprising a piezoelectricactuator as set forth in the twenty-first invention, and a metallic inkflow path forming member formed on a lower surface of the bottomelectrode and having an ink flow path therein, wherein the cap member isjoined, by welding, to the ink flow path forming member.

Since the cap member is joined to the ink flow path forming member bywelding, this eliminates the need for separate provision of a cap memberfixing means. Accordingly, the number of component parts of the ink jethead is reduced.

Further, since the cap member is joined to the ink flowpath formingmember by welding, this makes it possible to prevent entrance ofmoisture from outside the closed space into the closed space frombetween the cap member and the ink flow path forming member.Accordingly, dielectric breakdown due to moisture is effectivelyprevented from occurring.

A forty-seventh invention is an ink jet head comprising a piezoelectricactuator as set forth in the twenty-second invention, and a metallic inkflow path forming member formed on a lower surface of the bottomelectrode and having an ink flow path therein, wherein the cap member isjoined, by welding, to the ink flow path forming member.

Accordingly, the forty-seventh invention provides the sameoperation/working-effect that the forty-sixth invention provides.

A forty-eighth invention is an ink jet head comprising a piezoelectricactuator as set forth in the twenty-third invention, and a metallic inkflow path forming member formed on a lower surface of the bottomelectrode and having an ink flow path therein, wherein the cap member isjoined, by welding, to the ink flow path forming member.

Accordingly, the forty-eighth invention provides the sameoperation/working-effect that the forty-sixth invention provides.

A forty-ninth invention is an ink jet head comprising a piezoelectricactuator as set forth in the twenty-fourth invention, and a metallic inkflow path forming member formed on a lower surface of the bottomelectrode and having an ink flow path therein, wherein the cap member isjoined, by welding, to the ink flow path forming member.

Accordingly, the forty-ninth invention provides the sameoperation/working-effect that the forty-sixth invention provides.

In a fiftieth invention according to the forty-sixth invention, a stepportion is formed in an upper peripheral area of the ink flow pathforming member and the cap member is joined, by welding, to the stepportion of the ink flow path forming member.

Since the cap member is joined to the step portion of the ink flow pathforming member by welding, the cap member and the piezoelectric actuatormain body are in non-contact with each other. Accordingly, it ispossible to prevent the cap member from interfering with the operationof the piezoelectric actuator main body.

In a fifty-first invention according to the forty-seventh invention, astep portion is formed in an upper peripheral area of the ink flow pathforming member and the cap member is joined, by welding, to the stepportion of the ink flow path forming member.

Accordingly, the fifty-first invention provides the sameoperation/working-effect that the fiftieth invention provides.

In a fifty-second invention according to the forty-eighth invention, astep portion is formed in an upper peripheral area of the ink flow pathforming member and the cap member is joined, by welding, to the stepportion of the ink flow path forming member.

Accordingly, the fifty-second invention provides the sameoperation/working-effect that the fiftieth invention provides.

In a fifty-third invention according to the forty-ninth invention, astep portion is formed in an upper peripheral area of the ink flow pathforming member and the cap member is joined, by welding, to the stepportion of the ink flow path forming member.

Accordingly, the fifty-third invention provides the sameoperation/working-effect that the fiftieth invention provides.

In a fifty-fourth invention according to the thirty-eighth invention,one or more ink supply openings for supplying of ink to the ink flowpath are opened in a surface of the ink flow path forming member, andsaid cap member is fixed to a region of the ink flow path forming membersurface other than where the ink supply openings are provided.

Incidentally, an ink tank for storing ink is connected to each inksupply opening. And, when the ink held in the ink tank is used up, theink tank must be replaced with a new one. If the cap member is mountedin a surface region of the ink flow path forming member where the inksupply openings are provided, this impedes the replacing of an ink tank.

On the other hand, in accordance with the present invention, the capmember is fixed in a surface region of the ink flow path forming memberother than where the ink supply openings are provided. Therefore, thereplacing of an ink tank will not be impeded by the cap member. Thistherefore facilitates ink tank replacement.

In a fifty-fifth invention according to the thirty-ninth invention, oneor more ink supply openings for supplying of ink to the ink flow pathare opened in a surface of the ink flow path forming member, and saidcap member is fixed to a region of the ink flow path forming membersurface other than where the ink supply openings are provided.

Accordingly, the fifty-fifth invention provides the sameoperation/working-effect that the fifty-fourth invention provides.

In a fifty-sixth invention according to the fortieth invention, one ormore ink supply openings for supplying of ink to the ink flow path areopened in a surface of the ink flow path forming member, and said capmember is fixed to a region of the ink flow path forming member surfaceother than where the ink supply openings are provided.

Accordingly, the fifty-sixth invention provides the sameoperation/working-effect that the fifty-fourth invention provides.

In a fifty-seventh invention according to the forty-first invention, oneor more ink supply openings for supplying of ink to the ink flow pathare opened in a surface of the ink flow path forming member, and saidcap member is fixed to a region of the ink flow path forming membersurface other than where the ink supply openings are provided.

Accordingly, the fifty-seventh invention provides the sameoperation/working-effect that the fifty-fourth invention provides.

A fifty-eighth invention is an ink jet head according to thethirty-eighth invention which further comprises an electrodeinterconnection for transmission of electrical signals to the topelectrode, wherein the electrode interconnection is interposed betweenthe cap member and the ink flow path forming member.

A fifty-ninth invention is an ink jet head according to the thirty-ninthinvention which further comprises an electrode interconnection fortransmission of electrical signals to the top electrode, wherein theelectrode interconnection is interposed between the cap member and theink flow path forming member.

A sixtieth invention is an ink jet head according to the fortiethinvention which further comprises an electrode interconnection fortransmission of electrical signals to the top electrode, wherein theelectrode interconnection is interposed between the cap member and theink flow path forming member.

A sixty-first invention is an ink jet head according to the forty-firstinvention which further comprises an electrode interconnection fortransmission of electrical signals to the top electrode, wherein theelectrode interconnection is interposed between the cap member and theink flow path forming member.

A sixty-second invention is an ink jet type recording device comprisingan ink jet head according to the thirty-third invention.

A sixty-third invention is an ink jet type recording device comprisingan ink jet head according to the thirty-fourth invention.

A sixty-fourth invention is an ink jet type recording device comprisingan ink jet head according to the thirty-fifth invention.

A sixty-fifth invention is an ink jet type recording device comprisingan ink jet head according to the thirty-sixth invention.

A sixty-sixth invention is an ink jet type recording device comprisingan ink jet head according to the thirty-seventh invention.

A sixty-seventh invention is a method of manufacturing a piezoelectricactuator, comprising the steps of: subjecting a piezoelectric actuatormain body, formed by laminating together a bottom electrode, apiezoelectric element, and a top electrode in sequence, to adehumidification process; placing a moisture absorbent having an abilityto absorb moisture within a cap member; and enclosing at least a surfaceof the piezoelectric actuator main body on the side of the top electrodeby the cap member.

A sixty-eighth invention is a method of manufacturing a piezoelectricactuator, comprising the steps of: placing a moisture absorbent havingan ability of absorb moisture within a cap member; enclosing at least asurface of a piezoelectric actuator, formed by laminating together abottom electrode, a piezoelectric element, and a top electrode insequence, on the side of the top electrode by the cap member; andleaving the piezoelectric actuator main body as it is until the moistureabsorbent absorbs a predetermined amount of moisture in a closed spacebetween the piezoelectric actuator main body and the cap member.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic construction diagram of an ink jet type recordingdevice according to an embodiment of the present invention;

FIG. 2 is a perspective view showing, in partially broken manner, an inkjet head according to the embodiment;

FIG. 3 is a cross-sectional view of the ink jet head according to theembodiment;

FIG. 4 is a top plan view of the ink jet head according to theembodiment;

FIG. 5 is a schematic top plan view of the ink jet head according to theembodiment;

FIG. 6 graphically shows a relationship between the relative humiditywithin a closed space according to the embodiment, and the rate ofoccurrence of dielectric breakdown;

FIG. 7 graphically shows a relationship between the amount of moistureabsorption of a moisture absorbent according to the embodiment, and therate of occurrence of dielectric breakdown;

FIG. 8 graphically shows a relationship between the permeability ofwater vapor in an interior surface of a head block according to theembodiment, and the rate of occurrence of dielectric breakdown;

FIG. 9 is a first part of a manufacturing process diagram of the ink jethead according to the embodiment;

FIG. 10 is a second part of the manufacturing process diagram of the inkjet head according to the embodiment;

FIG. 11 is a cross-sectional view of a part of the ink jet headaccording to the embodiment;

FIG. 12 is a cross-sectional view of the ink jet head according to theembodiment; and

FIG. 13 is a cross-sectional view of an ink jet head according to anembodiment of the present invention.

BEST MODE FOR CARRYING OUT INVENTION

Embodiment 1

As shown in FIG. 1, an ink jet head 1 of the present embodiment,incorporated into an ink jet printer 3 as an ink jet type recordingdevice, effects recording by shooting droplets of ink onto a recordingmedium 5 such as a sheet of paper.

The ink jet head 1, mounted on a carriage 9 which travels to and froalong a carriage shaft 7, reciprocates in a primary scan direction X,together with the carriage 9. A roller 10 is so constructed as to conveythe recording medium 5 in a secondary scan direction Y every time thecarriage 9 travels a scan distance in the primary scan direction X.

As shown in FIGS. 2 and 3, the ink jet head 1 comprises a head main bodypart 17 in which are formed a common ink chamber 11, a plurality ofpressure chamber recessed portions 13 (not shown in FIG. 3), and aplurality of nozzles 15, and a piezoelectric actuator 21 for applyingvoltage to the ink within a pressure chamber 19. The pressure chamberrecessed portions 13 are arrayed at predetermined intervals along thesecondary scan direction Y. The pressure chamber recessed portions 13thus arrayed constitute rows of pressure chamber recessed portions. Theink jet head 1 of the present embodiment has two pressure chamberrecessed portion rows. Each pressure chamber recessed portion 13 has anopening cross section (X-Y cross section) shaped like a rectangularwhich is oblong in the primary scan direction X. Note that the ink flowpath as referred to in the present invention is made up of the commonink chamber 11 and an ink supply path 41 which will be described later.

The head main body part 17 is made up of a pressure chamber formingplate 35 of Si, an ink flow path forming plate 37 of stainless steel,and a nozzle plate 39 of stainless steel. Formed in the pressure chamberforming plate 35 is the pressure chamber 19. An ink supply opening 23connecting together the common ink chamber 11 and the pressure chamber19 is formed at one longitudinal end (right-hand side end in FIG. 2) ofthe bottom of each pressure chamber recessed portion 13 in the ink flowpath forming plate 37. Formed at the other longitudinal end (left-handside end in FIG. 2) is an ink flow path 25 connecting together thepressure chamber 19 and the nozzles 15. In addition, the common inkchamber 11 extending in the secondary scan direction Y is formed in theink flow path forming plate 37.

As shown in FIG. 4, one end of the common ink chamber 11 (upper end inFIG. 4) is connected to the ink supply path 41. The ink supply path 41is so formed as to extend over the pressure chamber forming plate 35 andthe ink flow path forming plate 37 in a Z direction. One end of the inksupply path 41 is connected to the common ink chamber 11 and the otherend thereof is connected to an ink tank (not shown). As shown in FIG. 3,the nozzle plate 39 extends longer than the piezoelectric actuator 21,the pressure chamber forming plate 35, and the ink flow path formingplate 37 in the primary scan direction X as well as in the secondaryscan direction Y. Furthermore, as shown in FIGS. 2 and 3, the nozzles 15are formed in the nozzle plate 39. In addition, the ink flow pathforming member as referred to in the present invention is made up of thepressure chamber forming plate 35, the ink flow path forming plate 37,and the nozzle plate 39, and the step portion is formed by a stepbetween the ink flow path forming plate 37 and the nozzle plate 39, andthe ink supply opening is formed by an end portion of the ink supplypath 41 on the side of the ink tank.

As shown in FIGS. 2 and 3, the piezoelectric actuator 21 has: apiezoelectric actuator part 22 made up of a common electrode 27 of Crhaving a thickness of from 1 to 10 μm, a piezoelectric element 29 ofPb(Zr, Ti)O₃ having a thickness of 3.0 μm and formed on the commonelectrode 27, and an individual electrode 33 of Pt having a thickness of0.1 μm and formed on the piezoelectric element 29; an electricalinterconnection joint part 43 formed on the individual electrode 33; anelectrical interconnection 45 formed on the electrical interconnectionjoint part 43; a head block 47 fixed to the nozzle plate 39 through theelectrical interconnection 45; and a PI tape 49 disposed within the headblock 47. Note that the electrical interconnection joint part 43, theelectrical interconnection 45, the head block 47, and the PI tape 49 arenot represented diagrammatically in FIG. 2. The common electrode 27 actsalso as a vibrating plate. The piezoelectric element 29 and theindividual electrode 33 are so disposed as to be located at areascorresponding to their respective pressure chamber recessed portions 13of the head main body part 17. The individual electrode 33 and theelectrical interconnection 45 are connected together through theelectrical interconnection joint part 43. The electrical interconnection45 is connected to one end of each individual electrode 33 as well as toa voltage input terminal part (not shown) for impressing voltage on eachindividual electrode 33. In addition, the bottom electrode as referredto in the present invention is formed by the common electrode 27, andthe top electrode is formed by the individual electrode 33, and thepiezoelectric actuator main body is formed by the piezoelectric actuatorpart 22, and the cap member is formed by the head block 47, and thedividing member is formed by the PI tape 49.

As shown in FIGS. 3 and 5, an upper surface portion 47 a of the headblock 47 is shaped like a rectangle. A step portion 47 d is formed in aside surface portion 47 c of the head block 47. In other words, the stepportion 47 d of the head block 47 bends at right angles relative to anupper and a lower portion of the side surface portion 47 c. An endportion of the head block 47 bends at right angles relative to the sidesurface portion 47 c to form a collar portion 47 b. In the way asdescribed above, the head block 47 is shaped like a hat. In addition,the head block 47 is made of stainless steel.

The head block 47 is fixed, through a substantially O-shaped firstO-ring 51 of resin, the electrical interconnection 45, and a secondO-ring 53, to an upper surface of the nozzle plate 36 by presser jigs 55such as turn fasteners, push rivets or the like. More specifically, thefour corners of the collar portion 47 b of the head block 47 and theupper surface four corners of the nozzle plate 39 are fixed together bythe four presser jigs 55. In addition, a lower end of each presser jig55 lies above the lower surface of the nozzle plate 39.

A closed space 57 is formed within the head block 47. And, thepiezoelectric actuator part 22 is sealed within the closed space 57. Inaddition, the head block 47 is in non-contact with the piezoelectricactuator part 22. Furthermore, as shown in FIG. 4, the head block 47 isdisposed on a region (indicated by a chain double-dashed line of FIG. 4)of the upper surface of the head main body part 17 other than where theink supply path 41 is formed. Note that diagrammatic representation ofthe head block 47 is omitted in FIG. 4.

Further, as has been described above, the head block 47 is made ofstainless steel, and the permeability of water vapor in the interiorsurface of the head block 47 is not more than 7.0 g/m²·24 hr·atm.Generally, the permeability of water vapor indicates the amount of watervapor passing through the head block 47 of a unit area. Furthermore, theinterior surface of the head block 47 is a surface of the head block 47in contact with the closed space 57. In the present embodiment,particularly the permeability of water vapor is defined as the amount ofwater vapor passing through the head block 47 with an interior surfacearea of 1 m² per 24 hours in a 1-atm environment. Note that thethickness of the head block 47 is unconsidered here.

As shown in FIG. 3, the PI tape 49 is formed of a resin material and isso disposed, in spanned manner, at the step portion 47 d of the headblock 47 as not to come into contact with the piezoelectric actuatorpart 22. Stated another way, the PI tape 49 is affixed to the stepportion 47 d of the head block 47. And, the PI tape 49 divides theclosed space 57 into two sections. Of these divided sections of theclosed space 57, the one on the side of the head block 47 (upper sectionin FIG. 3) constitutes a first closed space 57 a and the other on theside of the piezoelectric actuator part 22 (lower section in FIG. 3)constitutes a second closed space 57 b. The moisture absorbent 52 issealed within the first closed space 57 a. The moisture absorbent 52has, as an indication of the efficiency of moisture absorption, acoefficient of moisture absorption of not less than 5 wt. % in ameasurement environment of 25° C., 1 atm, and 80% relative humidity. Inthe present embodiment, the moisture absorbent 52 comprises granulatedsilica gel and is supported by the PI tape 49. Furthermore, one or morethrough holes 50 for establishing communication between the first closedspace 57 a and the second closed space 57 b are formed in the PI tape49. The bore diameter of the through holes 50 is smaller than thediameter of the moisture absorbent 52.

Operating Method of Ink Jet Head

Here, an operating method of the ink jet head according to the presentembodiment will be described. In the first place, voltage is impressedon the common electrode 27 as well as on the individual electrode 33.This voltage impression on both the electrodes 27 and 33 causes thepiezoelectric element 29 to expand and contract. Suchexpansion/contraction is restricted by the common electrode 27 servingalso as a vibrating plate, thereby causing the piezoelectric actuatorpart 22 to bend and deform in the lamination direction. Suchbending/deformation causes the volume of the pressure chamber 19 to varyand, as a result, ink in the inside of the pressure chamber 19 flowsthrough the ink flow path 25 and is emitted from the nozzle 15.

Method for Evaluation of Dielectric Breakdown Occurrence Rate

In the present experiments, a plurality of ink jet heads 1 were preparedas samples for the purpose of evaluation of the rate of occurrence ofdielectric breakdown to be hereinafter described. Each ink jet head 1prepared comprises: a piezoelectric actuator part 22 formed bylaminating together, in sequence, a head main body part 17, a commonelectrode 27, a piezoelectric element 29, and an individual electrode33; a head block 47 fixed to the head main body part 17; and a moistureabsorbent 52 sealed within a closed space 57 defined between the headmain body part 17 and the head block 47. Each ink jet head 1 is made upof 400-pin nozzles 15 and piezoelectric actuator parts 22. Additionally,these ink jet heads 1 were prepared in three types, namely ink jet heads1 having a closed space 57 the volume of which is 1.96×10⁻⁶ m³, ink jetheads 1 having a closed space 57 the volume of which is 2.93×10⁻⁵ m³,and ink jet heads 1 having a closed space 57 the volume of which is3.72×10⁻⁵ m³. And, the ink jet heads 1 of each type were placed in ameasurement environment of 60° C. and 1 atm, and the closed spaces 57 ofthe ink jet heads 1 were at different relative humidity levels. Then, adc voltage of 35V was impressed between the common electrode 27 and theindividual electrode 33 of each ink jet head 1 for 150 hours, and pinsbroken in the electrodes 27 and 33 or pins broken in the piezoelectricelement 29 due to the occurrence of dielectric breakdown were counted.And, in each ink jet head 1, the ratio of the number of broken pins tothe total number of pins was calculated and the result was used as adielectric breakdown occurrence rate.

The results of the above-described measurements show clearly that therate of occurrence of dielectric breakdown is 0% when the relativehumidity within the closed space 57 is not less than 0% nor more than20% (see FIG. 6). Additionally, it becomes obvious that, when therelative humidity within the closed space 57 is not less than 20% normore than 40%, the rate of occurrence of dielectric breakdown issubstantially 0%.

The foregoing measurements were carried out in an environment of 60° C.However, even in environments other than the 60° C. environment, therate of occurrence of dielectric breakdown is 0% if the relativehumidity within the closed space 57 is not less than 0% nor more than20%. For the closed space 57 of 1 m³, the amount of saturation watervapor is about 130 g when the temperature is 60° C. and the atmosphericpressure is 1 atm. Here, if the relative humidity within the closedspace 57 is 20%, then the amount of water vapor present within theclosed space 57 is: 130×0.20=26 g. Therefore, the rate of occurrence ofdielectric breakdown becomes substantially 0% as long as the amount ofwater vapor present within the closed space 57 of 1 m³ in an environmentof 60° C. and 1 atm is not more than 26 g.

Additionally, in order to examine the relationship between the amount ofmoisture absorption of the moisture absorbent 52 and the rate ofoccurrence of dielectric breakdown, measurements, in which a directcurrent voltage of 35V was impressed between the common electrode 27 andthe individual electrode 33 of each ink jet head 1 for 150 hours, werecarried out in addition to the foregoing measurements, for dielectricbreakdown occurrence rate calculation. Here, the amount of moistureabsorption is represented by: (the weight of the moisture absorbent 52after moisture absorption−the weight of the moisture absorbent 52 beforemoisture absorption)/the weight of the moisture absorbent 52 beforemoisture absorption.

The results of the above measurements show clearly that the rate ofoccurrence of dielectric breakdown is 0% when the amount of moistureabsorption of the moisture absorbent 52 is not less than 0 wt. % normore than 20 wt. % (see FIG. 7).

Additionally, a plurality of ink jet heads 1 each having a differentwater vapor permeability in the interior surface of the head block 47thereof were prepared for different measurements from the foregoingmeasurements. More specifically, in a high temperature and humiditymeasurement environment of 80% relative humidity and 60° C., a directcurrent voltage of 35V was impressed between the common electrode 27 andthe individual electrode 33 of each ink jet head 1 for 150 hours, fordielectric breakdown occurrence rate calculation.

The results of the above measurements show clearly that the rate ofoccurrence of dielectric breakdown is 0% when the permeability of watervapor in the interior surface of the head block 47 is not more than 7.0g/m²·24 hr·atm (see FIG. 8).

Method of Manufacture for Ink Jet Head

Referring next to FIGS. 9 and 10, a method of manufacturing an ink jethead 1 will be described.

In the first place, a common electrode 27 is formed on a pressurechamber forming plate 35 (see FIG. 9A).

In the next place, a piezoelectric element 29 is formed on the commonelectrode 27 by sputtering, vapor deposition, or the like (FIG. 9B). Inthe course of such formation, there is the possibility that either adefective portion 63 is formed within the piezoelectric element 29 ordefective portions 65 and 67 continuously extending through the commonelectrode 27 and the piezoelectric element 29 are formed. The defectiveportions 63 and 65 are pinholes caused by contaminants adhered onto thepressure chamber forming plate 35 when sputtering the piezoelectricelement 29. On the other hand, the defective portion 67 is a voidresulting from abnormal growth of the piezoelectric element 29 caused bya contaminant 69 adhered onto the pressure chamber forming plate 35. Thepinholes 63 and 65 and the void 67 are from 0.1 to 10 μm in openingdiameter.

Next, a top electrode 31 is formed on the piezoelectric element 29 bysputtering, vapor deposition, or the like (FIG. 9C). Then, the topelectrode 31 and the piezoelectric element 29 are individualized to formindividual electrodes 33 and the piezoelectric element 29 located atother than where the individual electrodes 33 is formed is removed.Here, such individualization is done by etching or the like.

Thereafter, the ink jet head 1 which has undergone the foregoing steps,i.e., the ink jet head 1 on which a head block 47 has not been mountedyet is subjected to a dehumidification process. More specifically, theink jet head 1 is heated at 100 to 150° C. Furthermore, the ink jet head1 is air evacuated under vacuum.

Next to the above, the pressure chamber forming plate 35 is worked toform a pressure chamber 19 (FIG. 9D). In order to prevent the commonelectrode 27 from becoming damaged when the pressure chamber 19 isformed by working the pressure chamber forming plate 35, a stopper layer(not shown) may be provided between the pressure chamber forming plate35 and the common electrode 27.

Thereafter, an integrated combination of an ink flow path forming plate37 in which are formed an ink flow path 25 and so on and a nozzle plate39 in which is formed a nozzle 15 is mounted onto the pressure chamberforming plate 35 (FIG. 9E). Thereafter, an electrical interconnectionjoint part 43 and an electrical interconnection 45 are formed, in thatorder, on the individual electrode 33, which is not representeddiagrammatically.

Next, a moisture absorbent 52 is fed within a head block 47 preparedseparately from the ink jet head 1 (FIG. 10A). Thereafter, a PI tape 49is affixed within the head block 47 so that the moisture absorbent 52 issealed within the head block 47.

Finally, as shown in FIG. 10B, the nozzle plate 39 of the ink jet head 1and the collar portion 47 b of the head block 47 are fixed together.Here, diagrammatic representation of the first O-ring 51, the secondO-ring 53, and the presser jig 55 is omitted. In this way, the formationof the ink jet head 1 is completed.

Before being put in actual operation, the formation-completed ink jethead 1 is left as it is in a low humidity environment for a certainperiod of time until the moisture absorbent 52 absorbs a predeterminedamount of moisture within the closed space 57.

After the above-described steps, it is achieved that the relativehumidity within the closed space 57 of the ink jet head 1 is not lessthan 0% nor more than 20% and the amount of moisture absorption of themoisture absorbent 52 is not less than 0 wt. % nor more than 20 wt. %.

As has been described above, in accordance with the present embodiment,the ink jet head 1 on which the head block 47 has not been mounted yetis subjected to a heating process at 100 to 150° C. and to an airexcavating process under vacuum. Therefore, even when a void 67 andpinholes 63 and 65 occur within the piezoelectric element 29, therebyresulting in entrance of moisture thereinto, the moisture is preremovedbefore the head block 47 is mounted on the ink jet head 1. Accordingly,dielectric breakdown due to moisture is prevented from occurring.

Besides, before being put in actual operation, the formation-completedink jet head 1 is left as it is in a low humidity environment for acertain period of time until the moisture absorbent 52 absorbs apredetermined amount of moisture within the closed space 57, therebymaking it possible for the moisture absorbent 52 to absorb moisturewithin the closed space 57 before the ink jet head 1 is brought intoactual operation. Accordingly, dielectric breakdown due to moisture isprevented from occurring when the ink jet head 1 is put in actualoperation.

Furthermore, since the moisture absorbent 52 is sealed within the firstclosed space 57 a by the PI tape 49, this makes it possible to preventthe moisture absorbent 52 and the piezoelectric actuator part 22 fromcoming into contact with each other. Accordingly, it is possible toprevent the piezoelectric actuator part 22 from becoming damaged by themoisture absorbent 52.

Moreover, since the moisture absorbent 52 is supported by the PI tape49, this eliminates the need for separate provision of a supportingmeans for supporting the moisture absorbent 52. Accordingly, the numberof component parts of the ink jet head 1 is reduced.

Furthermore, the PI tape 49, since it is formed of resin material, isdeformed easily. Therefore, the PI tape 49 can be disposed within thehead block 47 by making a change in the shape of the PI tape 49,regardless of the shape of the inside of the head block 47. Thisfacilitates the PI tape 49 to be disposed within the head block 47.

Moreover, since one or more through holes 50 are formed in the PI tape49, this makes it possible for the moisture absorbent 52 sealed withinthe first closed space 57 a to effectively absorb moisture within thesecond closed space 57 b through the through holes 50. Accordingly,dielectric breakdown due to moisture is prevented from occurring.

Furthermore, since the head block 47 is formed of stainless steel, thismakes it possible to prevent entrance of water vapor into the closedspace 57. Accordingly, dielectric breakdown due to moisture is preventedfrom occurring.

In addition, since the head block 47 is fixed to the upper surface ofthe nozzle plate 39, this eliminates the need for separate provision ofa fixing means for fixing the head block 47 to the nozzle plate 39.Accordingly, the number of component parts of the ink jet head 1 isreduced.

Furthermore, since the nozzle plate 39 extends longer than thepiezoelectric actuator 21 in the primary scan direction X as well as inthe secondary scan direction Y, the head block 47 fixed to the fourcorners of the upper surface of the nozzle plate 39 will not come intocontact with the piezoelectric actuator part 22. This accordinglyprevents the head block 47 from interfering with the operation of thepiezoelectric actuator part 22.

Moreover, since the head block 47 is mounted on a region of the uppersurface of the head main body part 17 other than where the ink supplypath 41 is provided, this ensures that replacement of an ink tank willnot be impeded by the head block 47. This accordingly facilitates inktank replacement.

In the present embodiment, the head block 47 is fixed to the uppersurface of the nozzle plate 39 by the presser jig 55 through the firstO-ring 51, the electrical interconnection 45, and the second O-ring 53.Alternatively, pins, screws, or the like may be used in place of thepresser jig 55. In addition, a retaining jig, a pinching jig, anadhesive, or the like may be used instead of the presser jig 55 forfixing the head block 47 to the nozzle plate 39.

In the present embodiment, the head block 47 is fixed to the uppersurface of the nozzle plate 39 by the presser jig 55, which is, however,not deemed restrictive. For example, as shown in FIG. 11, the head block47 may be fixed to the electrical interconnection 45 formed on theindividual electrode 33 by an adhesive 59. Furthermore, as shown in FIG.12, the head block 47 and the ink flow path forming plate 37 are fixedby a presser jig 61. In this case, the ink flow path forming plate 37extends longer than the piezoelectric actuator 21, the pressure chamberforming plate 35, and the nozzle plate 39 in the primary scan directionX as well as in the secondary scan direction Y.

Furthermore, in the present embodiment, the head block 47 is fixed tothe upper surface of the nozzle plate 39 by the presser jig 55.Alternatively, the head block 47 may be fixed to a side surface of thenozzle plate 39.

Additionally, in the present embodiment, the nozzle plate 39 extendslonger than the piezoelectric actuator 21, the pressure chamber formingplate 35, and ink flow path forming plate 37 in the primary scandirection X as well as in the secondary scan direction Y. However, thepressure chamber forming plate 35, the ink flow path forming plate 37,and the nozzle plate 39 may extend substantially the same length in theprimary scan direction X as well as in the secondary scan direction Y.In this case, the head block 47 is fixed to the upper surface of thepressure chamber forming plate 35.

In the present embodiment, the head block 47 is formed of stainlesssteel. Alternatively, the head block 47 may be formed of resin material.In this case, preferably the resin material has a thickness of not lessthan 1 mm.

Embodiment 2

An ink jet head according to the present embodiment employs substantialthe same construction as the ink jet head of the first embodiment.Hereinafter, constructional differences from the first embodiment willbe described.

In the present embodiment, the collar portion 47 b of the head block 47and an outer edge portion of the upper surface of the nozzle plate 39are metal welded together, as shown in FIG. 13.

In the present embodiment, the collar portion 47 b of the head block 47and the upper surface outer edge portion of the nozzle plate 39 aremetal welded together, thereby preventing entrance of water vapor intothe closed space 57 from between the collar portion 47 b of the headblock 47 and the nozzle plate 39. Accordingly, dielectric breakdown dueto moisture is prevented from occurring.

Additionally, in the present embodiment the collar portion 47 b of thehead block 47 and the upper surface outer edge portion of the nozzleplate 39 are metal welded together. Alternatively, it may be arrangedsuch that the collar portion 47 b of the head block 47 and the uppersurface of the ink flow path forming plate 37 are metal welded. In thiscase, the metal-welded ink flow path forming plate 37 extends longerthan the piezoelectric actuator 21, the pressure chamber forming plate35, and the nozzle plate 39 in the primary scan direction X as well asin the secondary scan direction length Y. Furthermore, in the case thepressure chamber forming plate 35 is formed of metal, it may be arrangedsuch that the collar portion 47 b of the head block 47 and the uppersurface of the pressure chamber forming plate 35 are metal weldedtogether. In this case, the metal-welded pressure chamber forming plate35 extends longer than the piezoelectric actuator 21, the ink flow pathforming plate 37, and the nozzle plate 39 in the primary scan directionlength X as well as in the secondary scan direction length Y.

Besides, in each of the foregoing embodiments the head block 47 isshaped like a hat. However, the head block 47 may assume any shape aslong as it is able to enclose a surface of the piezoelectric actuatorpart 22 on the side of the individual electrode 33.

In addition to the above, each of the foregoing embodiments usesgranulated silica gel as the moisture absorbent 52. Alternatively, themoisture absorbent 52 may be implemented by silica gel in the form of asheet. Furthermore, moisture absorbents other than silica gel (e.g.,alumina gel, calcium chloride, molecular sieve et cetera) may be used.

Additionally, in each of the foregoing embodiments the dividing memberaccording to the present invention is formed by the PI tape 49 of resin.Alternatively the dividing member may be formed of resin materials otherthan the PI tape 49. Further, the dividing member may be formed of metalor the like. In this case, turn fasteners, push rivets, or the like formetal fixation within the head block 47 are used.

Furthermore, in each of the foregoing embodiments the common electrode27 serves also as a vibrating plate. Alternatively, it may be arrangedsuch that a vibrating plate is provided separately from the commonelectrode 27. In this case, the vibrating plate is formed on thepressure chamber forming plate 35, the individual electrode 33, or othercomponent.

Additionally, in each of the foregoing embodiments the common electrode27 is formed on the pressure chamber forming plate 35. Alternatively, itmay be arranged such that the individual electrode 33 is formed on thepressure chamber forming plate 35. In this case, the common electrode 27is formed on the piezoelectric element 29.

Furthermore, the components, i.e., the common electrode 27, thepiezoelectric element 29, the individual electrode 33, the pressurechamber forming plate 35, the ink flow path forming plate 37, the nozzleplate 39 and so on, may differ in forming material and thickness fromtheir counterparts of each of the foregoing embodiments.

Additionally, each of the foregoing embodiments forms the ink jet head 1by employing the above-described forming method. Alternatively, otherforming methods, e.g., a so-called transfer method, may be used tomanufacture the ink jet head 1. A method of manufacturing the ink jethead 1 by means of a transfer technique will be described in brief. Inthe first place, an individual electrode, a piezoelectric element, and avibrating plate are laminated, in that order, on an MgO substrate. Inthis case, either the vibrating plate may act also as a common electrodeor a common electrode may be provided separately from the vibratingplate. This is followed by adhesion of a substrate in which a pressurechamber is formed onto the vibrating plate. Finally, the MgO substrateis removed.

Furthermore, in each of the foregoing embodiments theformation-completed ink jet head 1 is let stand in a low humidityenvironment for a certain period of time before being put in actualoperation. Instead, the ink jet head 1 may be subjected to an airevacuating process under vacuum.

In addition to the above, in each of the foregoing embodiments one ormore through holes 50 are formed through the PI tape 49; however, theprovision of through holes may be unnecessary.

Furthermore, the ink jet head 1 according to each of the foregoingembodiments has two rows of pressure chamber recessed portions.Alternatively, the number of pressure chamber recessed portion rows maybe one or not less than three. Additionally, the number of pressurechamber recessed portions 13 constituting a pressure chamber recessedportion row is arbitrary.

Additionally, in each of the foregoing embodiments, the PI tape 49 isdisposed in the step portion 47 d of the head block 47. The PI tape 49may be disposed anywhere within the head block 47 as long as it will notcome into contact with the piezoelectric actuator part 22.

INDUSTRIAL APPLICABILITY

As has been described above, the present invention is useful whenapplied to a printer for computers, facsimile machines, copyingmachines, et cetera.

The entire content of Priority Document No. 2002-181402 is incorporatedherein by reference.

1. A piezoelectric actuator comprising: a piezoelectric actuator mainbody having a bottom electrode, a piezoelectric element formed on saidbottom electrode, and a top electrode, formed on said piezoelectricelement, for impressing voltage on said piezoelectric element togetherwith said bottom electrode, a cap member for enclosing at least asurface of said piezoelectric actuator main body on the side of said topelectrode, and a moisture absorbent disposed in a closed space betweensaid piezoelectric actuator main body and said cap member and having anability to absorb moisture, wherein ambient relative humidity withinsaid closed space is not less than 0% nor more than 20% in a measurementenvironment of 60° C. and 1 atm, and said cap member is fixed onto asurface of said piezoelectric actuator main body.
 2. A piezoelectricactuator comprising: a piezoelectric actuator main body having a bottomelectrode, a piezoelectric element formed on said bottom electrode, anda top electrode, formed on said piezoelectric element, for impressingvoltage on said piezoelectric element together with said bottomelectrode, a cap member for enclosing at least a surface of saidpiezoelectric actuator main body on the side of said top electrode, anda moisture absorbent disposed in a closed space between saidpiezoelectric actuator main body and said cap member and having anability to absorb moisture, wherein said cap member has, in an interiorsurface thereof, a water vapor permeability of not more than 7 g/m²·24hr·atm, and said cap member is fixed onto a surface of saidpiezoelectric actuator main body.
 3. The piezoelectric actuator of claim1 further comprising an electrode interconnection, formed on said topelectrode, for transmission of electrical signals to said top electrode,wherein said electrode interconnection is interposed between said capmember and a surface of said piezoelectric actuator main body.
 4. Thepiezoelectric actuator of claim 2 further comprising an electrodeinterconnection, formed on said top electrode, for transmission ofelectrical signals to said top electrode, wherein said electrodeinterconnection is interposed between said cap member and a surface ofsaid piezoelectric actuator main body.
 5. An ink jet head comprising: apiezoelectric actuator comprising: a piezoelectric actuator main bodyhaving a bottom electrode, a piezoelectric element formed on said bottomelectrode, and a top electrode, formed on said piezoelectric element,for impressing voltage on said piezoelectric element together with saidbottom electrode, a cap member for enclosing at least a surface of saidpiezoelectric actuator main body on the side of said top electrode, anda moisture absorbent disposed in a closed space between saidpiezoelectric actuator main body and said cap member and having anability to absorb moisture, and an ink flow path forming member formedon a lower surface of said bottom electrode and having an ink flow paththerein, wherein ambient relative humidity within said closed space isnot less than 0% nor more than 20% in a measurement environment of 60°C. and 1 atm, a step portion is formed in an upper peripheral area ofsaid ink flow path forming member, said cap member fits with said stepportion of said ink flow path forming member, and said cap member isfixed onto a surface of said ink flow path forming member.
 6. An ink jethead comprising: a piezoelectric actuator comprising: a piezoelectricactuator main body having a bottom electrode, a piezoelectric elementformed on said bottom electrode, and a top electrode, formed on saidpiezoelectric element, for impressing voltage on said piezoelectricelement together with said bottom electrode, a cap member for enclosingat least a surface of said piezoelectric actuator main body on the sideof said top electrode, and a moisture absorbent disposed in a closedspace between said piezoelectric actuator main body and said cap memberand having an ability to absorb moisture, and an ink flow path formingmember formed on a lower surface of said bottom electrode and having anink flow path therein, wherein said cap member has, in an interiorsurface thereof, a water vapor permeability of not more than 7 g/m²·24hr·atm, a step portion is formed in an upper peripheral area of said inkflow path forming member, said cap member fits with said step portion ofsaid ink flow path forming member, and said cap member is fixed onto asurface of said ink flow path forming member.
 7. An ink jet headcomprising; a piezoelectric actuator comprising: a piezoelectricactuator main body having a bottom electrode, a piezoelectric elementformed on said bottom electrode, and a top electrode, formed on saidpiezoelectric element, for impressing voltage on said piezoelectricelement together with said bottom electrode, a cap member for enclosingat least a surface of said piezoelectric actuator main body on the sideof said top electrode, and a moisture absorbent disposed in a closedspace between said piezoelectric actuator main body and said cap memberand having an ability to absorb moisture, and a metallic ink flow pathforming member formed on a lower surface of said bottom electrode andhaving an ink flow path therein, wherein: ambient relative humiditywithin said closed space is not less than 0% nor more than 20% in ameasurement environment of 60° C. and 1 atm, said cap member is formedof a metal, a step portion is formed in an upper peripheral area of saidink flow path forming member, and said cap member is joined, by welding,to said step portion of said ink flow path forming member.
 8. An ink jethead comprising: a piezoelectric actuator comprising: a piezoelectricactuator main body having a bottom electrode, a piezoelectric elementformed on said bottom electrode, and a top electrode, formed on saidpiezoelectric element, for impressing voltage on said piezoelectricelement together with said bottom electrode, a cap member for enclosingat least a surface of said piezoelectric actuator main body on the sideof said top electrode, and a moisture absorbent disposed in a closedspace between said piezoelectric actuator main body and said cap memberand having an ability to absorb moisture, and a metallic ink flow pathforming member formed on a lower surface of said bottom electrode andhaving an ink flow oath therein, wherein: said cap member has, in aninterior surface thereof, a water vapor permeability of not more than 7g/m²·24 hr·atm, said cap member is formed of a metal, a step portion isformed in an upper peripheral area of said ink flow path forming member,and said cap member is joined, by welding, to said step portion of saidink flow path forming member.